1. Field of the Invention
The present invention relates to a magnet wire with high resistance to pulsed voltage surges.
More particularly, the present invention relates to a magnet wire, which is highly resistant to repetitive or pulsed high voltage spikes or surges, including at least a conductor and at least an insulating layer consisting of a composition which comprises at least a polymeric resin, at least a fluorinated filler and at least a non-ionic fluorinated surfactant.
The present invention also relates to a method for improving resistance to pulsed voltage surges of a magnet wire.
2. Description of the Related Art
Various types of variable frequency or pulse-width modulated (PWM) and/or inverter adjustable speed drives on AC motors and their affect on motor operation are known. PWM drives are known to have significant harmonics and transients which may alter the motor performance characteristics and life expectancy. The effects of maximum voltage, rate of rise, switching frequencies, resonances and harmonics have all been identified.
The PWM inverter is one of the newest and fastest evolving technologies in non-linear devices used in motor drive system. The motivation for using PWM inverters is speed control of an AC motor comparable to the prior mechanical or DC adjustable speed drives without loss of torque. With the increased emphasis of energy conservation and lower cost, the use of higher performance PWM drives has grown at an exponential rate. However, it has been found that these PWM drives cause premature failure of the magnet wire insulation systems used in such AC motors.
While it is known that conventional enamel compositions degrades when exposed to high voltage corona discharge, and that corona is discharged between adjacent windings of motor insulation, due to the inevitable voids and the high voltage ionization of air in the voids of the motor stator and rotor insulation windings, it has been found that insulation failure of motor driven by variable frequency, PWM and/or inverter drives is not primarily a corona insulation degradation mechanism.
As a matter of fact, corona ageing and magnet wire failure conditions may be distinguished from pulsed voltage surge ageing and magnet wire failure conditions. Corona ageing conditions occur in the presence of gas (usually air in magnet wire windings) at positions of localized high electrical stress (AC and DC), that is strong enough to break down or ionize the gas, to produce electron or ion energy strong enough to break down polymer chain or to create ionic radicals via chemical reactions. The chemical reactions result in polymer degradation. Corona discharge is a relatively “cold discharge” and temperature is usually not a substantial factor like in the case of pulsed voltage surges. Magnet wire ageing/failure due to corona is usually a long-term process.
In contrast, pulsed voltage surge ageing and magnet wire failure does not require the presence of a gas media. Pulsed voltage surge failure instead requires repetitive or pulsed voltage surges having relatively short rise times, or high voltage to rise time ratios, relatively high frequency of pulse and relatively high impulse energy, and occurs in relatively high temperatures generated thereby. Given high voltages and minimum rise times, pulsed voltage surge failure can occur relatively quickly, and is believed to be predominant cause of failure in variable frequency, PWM, and/or inverter driven motors.
Some efforts have been already made in order to overcome the above mentioned drawbacks.
For example, U.S. Pat. No. 4,546,041 relates to a corona-resistant wire enamel composition comprising a polyetherimide resin and from about 1% to about 35% by weight of dispersed alumina particles of a finite size less than about 0.1 μm, the alumina particles being dispersed therein by high shear mixing.
U.S. Pat. No. 6,060,162 relates to a pulsed voltage surge resistant magnet wire comprising a conductor, a continuous and concentric and flexible uniform coat of base insulation material superimposed on said conductor, an essentially continuous and concentric and uniform pulsed voltage surge shield superimposed on said coat, said shield comprising a continuous, concentric and essentially uniform layer of particulate material and binder overlaying said coat of insulation material, said shield having from about 1% to about 65% by weight of said particulate material uniformely disbursed through said binder, and a continuous and concentric and flexible and uniform top coat of insulation material superimposed on said shield, said conductor and said coats and shield being in compliance with AINSI/NEMA MW 100 1993. Said insulation material may be selected from polyamides, polyimides, polyamideimides, polyesters, polyesterimide, polyetherimides, polyesteramideimides, polyamide ester, polyimide esters, polyarylsulfones, polyvinyl acetals, polyurethanes, epoxy resins, acrylic resins and combination thereof. Said particulate material may be selected from metallic oxides such as, for example, titanium dioxide, alumina, silica, zirconium oxide, zinc oxide, iron oxide; various naturally occuring clays; and mixtures thereof.
U.S. Pat. No. 6,087,592 relates to an enamelled wire having high resistance to partial discharge including an electrical conductor and at least two layers of enamel on the conductor. At least one of these layers is made from resin charged with weakly conductive particles. The outhermost layer constitutes an overcoat and is made from thermo-adherent resin. At least the layer directly underlying the overcoat is made from the resin charged with said particles.
U.S. Pat. No. 6,100,474 relates to a magnet wire insulation designed to withstand voltage wave shapes present in inverter driven motors for a sustained period of time. A large surface area inorganic oxide, e.g. fumed silica, may be added into the magnet wire insulation for providing improved resistance to insulation degradation. Alternatively, a mixture of large surface area inorganic oxide with a low resistivity oxide, e.g. chromium oxide, provides a greater improvement in resistance to insulation degradation.
European patent application EP 287,813 relates to an electrical conductor provided with an electrical insulation surrounding the conductor and a surrounding protective layer which protects the insulation against degradation caused by corona. The protective layer consists of an organic polymer containing at least 10% by volume of a powdered filler material in the form of chromium oxide, iron oxide, or a mixture of chromium oxide and iron oxide.
Japanese patent application JP 50-13957 relates to polytetrafluoroethylene covered electrical wire having an intermediate covering layer of polyfluoroethylene propylene, which may contain a powder with conducting characteristics. It is said that, when the covered electrical wire is used under conditions of high electrical pressure, no insulation breakage due to corona discharged occurs and, moreover, that said electrical wire has better heat resistance, resistance to chemicals and other electrical characteristics.
Moreover, the magnet wires have to be endowed also with excellent windability, lubricity and abrasion resistance.
For example, Japanese patent application JP 56-106976 relates to an insulated electrical wire in which the conductor is coated and baked with an insulating layer containing from 0.1 to 10 wt parts with respect to 100 wt parts of the resin component of an ultra-fine tetrafluoroethylene resin having an average particle diameter of 10 μm or less. It is said that the insulated electrical wire has a low friction coefficient and better abrasion resistance. Moreover, no loss of heat resistance occurred.
Japanese Patent Application JP 3-245417 relates to a method of manufacturing an insulated electrical wire in which a fluororesin (for example, polytetrafluoroethylene resin) is dissolved in a solvent having a surface tension of 30 dyn/cm or less at 25° C. (for example, alcohol-based, ketone-based or aromatic hydrocarbon-based solvent). The resulting solution is used to coat the conductor. It is said that the fluororesin can be easily and homogeneously dispersed on the insulation coating, the external appearance of the insulated electrical wire is good and a stable low friction coefficient is obtained.
Japanese patent application JP 4-115411 relates to an insulated electrical wire comprising one or more insulating layers in which a powder comprising a mixture of polytetrafluoroethylene resin and polyethylene resin, said powder having a specific gravity within the range of from 0.98 to 1.11, is added to the most outer insulating layer. It is said that the insulated electrical wire has improved lubricity and abrasion resistance.
Japanese patent application JP 06-275128 relates to a resin composition for electrical insulation comprising 100 parts by weight of synthetic resin (for example, polyurethanes, polyesters, polyesterimides, polyamides), 0.1-10 parts by weight of tetrafluoroethylene and 0.1-10 parts by weight of an ammonium salt having the following formula CF3—(CF2)n—COONH4 wherein n is an integer from 1 to 20. It is said that the resin composition gives an insulated wire having good appearance, good sliding properties and good antifriction properties.
U.S. Pat. No. 4,716,079 relates to a magnet wire wherein insulating layer made of synthetic resin film (for example, polyvinylformals, polyesters, polyesterimides, polyesteramideimides, polyamideimides, polyimides, polyhydanthoins, polyurethanes, polyamides, epoxy resins, acrylic resins, polyetherirmides) is formed on the conductor and a lubricant layer made of an intimate mixture of natural wax as a major constituent and thermosetting and fluorocarbon resin compounded therewith is formed on the insulating layer. Thermosetting resins useful for this purpose are, for example, an ammonium or alcohol solution of shellac, a water dispersion of acrylic resin, an aqueous emulsion of water soluble phenolic resin. Fluorocarbon resins useful for this purpose are polytetrafluoroethylene (PTFE), a fluorinated ethylene-propylene copolymer (FEP), a polytrifluorochloroethylene (PTFCE). It is said that the magnet wire is excellent in windability, lubricity and abrasion resistance.